This invention relates to agglomerate abrasive grain comprising a plurality of abrasive particles bonded together via a sintered, alumina-based bonding material, and a method of making the agglomerate abrasive grain. The agglomerate abrasive grain can be incorporated into a variety of abrasive articles, including bonded abrasives, coated abrasives, nonwoven abrasives, and abrasive brushes.
There are a variety of abrasive particles (e.g., diamond particles, cubic boron nitride particles, fused abrasive particles (including fused alumina, heat treated fused alumina, fused alumina zirconia, and the like), and sintered, ceramic abrasive particles (including sol-gel-derived abrasive particles) known in the art. In some abrading applications, the abrasive particles are used in loose form or a slurry, while in others the particles are incorporated into abrasive products (including: bonded abrasives, coated abrasives and nonwoven abrasives).
Bonded abrasives typically comprise a plurality of abrasive particles bonded together to form a shaped mass. Coated abrasives typically comprise a plurality of abrasive particles bonded to a backing. Nonwoven abrasives typically comprise a plurality of abrasive particles bonded onto and into a lofty, porous, nonwoven substrate. Typical bonding materials for bonded abrasives are organic binders, vitreous binders, and metallic binders, while for coated and nonwoven abrasives they are typically organic binders. Criteria used in selecting abrasive particles used for a particular abrading application typically include: abrading life, rate of cut, substrate surface finish, grinding efficiency, and product cost.
The abrasive industry and their customers are continually looking for ways to improve one or more of these abrading criteria. For the past one hundred years or so, fused alumina abrasive particles have been widely utilized. Fused alumina abrasive particles are typically made by charging a furnace with an alumina source (such as aluminum ore or bauxite), as well as other desired additives, heating the material above its melting point, cooling the melt to provide a solidified mass, crushing the solidified mass into particles, and then screening and grading the particles to provide the desired abrasive particle size distribution. Over the past thirty years or so, there have been numerous inventions and developments concerning abrasive particles. One of these inventions was the development of co-fused alumina-zirconia abrasive particles. Additional information on alumina-zirconia abrasive particles can be found, for example, in U.S. Pat. No. 3,891,408 (Rowse et al.), U.S. Pat. No. 3,781,172 (Pett et al.), U.S. Pat. No. 3,893,826 (Quinan et al.), U.S. Pat. No. 4,126,429 (Watson), U.S. Pat. No. 4,457,767 (Poon et al.), and U.S. Pat. No. 5,143,522 (Gibson et al.).
Although fused alpha alumina abrasive particles and fused alumina-zirconia abrasive particles are still widely used in abrading applications (including those utilizing coated and bonded abrasive products), the premier abrasive particles for many abrading applications since about the mid-1980""s are sol-gel-derived alpha alumina particles (also referred to as sintered, ceramic alpha alumina particles). The sol-gel-derived alpha alumina abrasive particles may have a microstructure made up of very fine alpha alumina crystallites, with or without the presence of secondary phases added (see, e.g., U.S. Pat. No. 4,314,827 (Leitheiser et al.), U.S. Pat. No. 4,518,397 (Leitheiser et al.), U.S. Pat. No. 4,623,364 (Cottringer et al.), U.S. Pat. No. 4,744,802 (Schwabel), U.S. Pat. No. 4,770,671 (Monroe et al.), U.S. Pat. No. 4,881,951 (Wood et al.), U.S. Pat. No. 4,960,441 (Pellow et al.), (Pellow), U.S. Pat. No. 5,139,978 (Wood), U.S. Pat. No. 5,201,916 (Berg et al.), U.S. Pat. No. 5,366,523 (Rowenhorst et al.), U.S. Pat. No. 5,429,647 (Larmie), U.S. Pat. No. 5,547,479 (Conwell et al.), U.S. Pat. No. 5,498,269 (Larmie), U.S. Pat. No. 5,551,963 (Larmie), and U.S. Pat. No. 5,725,162 (Garg et al.)).
Coated abrasives tend to be xe2x80x9cmore flexiblexe2x80x9d than bonded abrasives; thus coated abrasives are widely utilized where the abrasive article needs to conform to the workpiece surface. Coated abrasives tend to have one or several layers of abrasive particles. It is generally preferred to orient these abrasive particles to enhance their cutting ability. However in some instances during the initial abrading, coated abrasives provide relatively very high cut rates. With time, the cut rate diminishes until the coated abrasive no longer provides acceptable cut rates.
To address the inconsistent cut rates with time, agglomerate abrasive grains have been developed (see, e.g., U.S. Pat. No. 3,928,949 (Wagner), U.S. Pat. No. 4,132,533 (Lohrner), U.S. Pat. No. 4,311,489 (Kressner), U.S. Pat. No. 4,393,021 (Eisenberg), U.S. Pat. No. 4,562,275 (Bloecher et al.), U.S. Pat. No. 4,799,939 (Bloecher et al.), U.S. Pat. No. 5,318,604 (Gorsuch), U.S. Pat. No. 5,550,723 (Holmes et al.), and U.S. Pat. No. 5,975,988 (Christiansen)). In the case of coated abrasives, these agglomerate abrasive grains are bonded to the backing to form an abrasive article. The agglomerate abrasive grains typically comprises a plurality of abrasive particles bonded together with a binder; usually an organic binder or inorganic binder.
One disadvantage with these abrasive agglomerate particles is that they are composite particles (i.e., abrasive particles and binder). The binder may adversely influence the abrading characteristics of the agglomerate grain. What is desired in the industry is a coated abrasive that provides a relatively long life and a cut rate that is relatively consistent over time.
Bonded abrasives are three dimensional in structure. Ideal bonded abrasive abrade the workpiece and when the abrasive particles are worn and dulled, these abrasive particles are expelled from the bonded abrasive to expose new, fresh cutting abrasive particles. In adequate adhesion between the abrasive particles and the bond material, can lead to premature release of the abrasive particles from the abrasive article. If the abrasive particles are prematurely released, the resulting bonded abrasive life is typically less than desired. What is desired in the industry is a bonded abrasive that exhibits good adhesion between the abrasive particles and the bond material.
In another aspect, to minimize inventory, and other associated manufacturing associated costs, it is typically preferred to make an abrasive grain that provides good grinding performance (e.g., long life, high cut rates, consistent cut rates, consistent surface finish and the like) in both coated abrasive and bonded abrasive applications. What is desired often in a coated abrasive is an abrasive grain that exhibits long life. What is desired often in a bonded abrasive is long life associated with good adhesion between the abrasive particles and the bonded abrasive binder.
The present invention provides agglomerate abrasive grain comprising a plurality of abrasive particles bonded together via sintered bonding material. The abrasive particles may comprise one or more abrasive particles including, but not limited to, fused aluminum oxide (including white fused alumina, heat-treated aluminum oxide, and brown aluminum oxide), silicon carbide, boron carbide, titanium carbide, diamond, cubic boron nitride, garnet, fused alumina-zirconia, sintered alpha alumina-based abrasive particles, and the like. Preferably, the bonding material comprises, on a theoretical oxide basis, at least 50 percent by weight Al2O3, based on the total metal oxide content of the bonding material. The bonding material may comprise, on a theoretical oxide basis, at least 60, 65, 70, 75, 80, 85, 90, 95, 97, 98, 99, 99.5, or even 100 (i.e., consists essentially of) percent by weight Al2O3, based on the total metal oxide content of the bonding material. In another aspect, the bonding material typically is at least 70, 75, 80 85, 90, 95, 97, 98, 99, 100 percent crystalline.
In some embodiments of the present invention, the agglomerate abrasive grain may comprise a plurality of abrasive particles bonded together with a sintered, crystalline ceramic bonding material, wherein the bonding material comprises, on a theoretical oxide basis, at least 50 percent by weight crystalline Al2O3, based on a total metal oxide content of the bonding material, and wherein the abrasive particles preferably have an average particle size of at least 5 micrometers. The average particle size of the particles in the agglomerate abrasive grain may be, at least 6, 7, 8, 9, 10, 15, 20, 25, or 30 micrometers, or larger.
In other embodiments of the present invention, the agglomerate abrasive grain according to the present invention may comprise a plurality of abrasive particles bonded together with a sintered, bonding material, wherein the bonding material comprises, on a theoretical oxide basis, at least 50 percent by weight crystalline Al2O3, based on a total metal oxide content of the bonding material, the abrasive particles have a density of at least 85% of theoretical density, and the agglomerate abrasive grain has a porosity value of at least 15 percent. Desirably, the abrasive particles have a density of at least 90% (at least 95%, at least 96%, at least 97%, at least 98%, at least 98.5%, at least 99%, or even at least 99.5%) of theoretical density. In another aspect, desirably the agglomerate abrasive grain has a porosity value of at least 15 (at least 20, at least 25, at least 30, at least 35, at least 40, at least 45, at least 50, at least 55, or at least 60) percent.
The agglomerate abrasive grain of the present invention typically have a porosity value (determined as described in the Examples, below) of, in increasing order of preference, at least 10%, 15%, or 20%. Preferably, the porosity value is, in increasing order of preference, in the range from about 15% to about 60%, about 20% to about 50%, or about 30% to about 45%.
In one exemplary embodiment, the present invention provides agglomerate abrasive grain comprising a plurality of sintered, crystalline abrasive particles bonded together via crystalline ceramic, metal oxide bonding material, wherein the bonding material comprises, on a theoretical oxide basis, at least 50 percent by weight Al2O3, based on the total metal oxide content of the bonding material, and wherein the agglomerate abrasive grain has a porosity value in the range from 10 to about 60 percent.
Another exemplary embodiment of the present invention provides agglomerate abrasive grain comprising a plurality of polycrystalline abrasive particles bonded together with a sintered, crystalline ceramic bonding material, wherein the bonding material comprises, on a theoretical oxide basis, at least 50 percent by weight crystalline Al2O3, based on a total metal oxide content of the bonding material, the abrasive particles have a density of at least 85% of theoretical density, and the agglomerate abrasive grain has a porosity value of at least 10 percent.
Embodiments of abrasive grain according to the present invention may have an abrasive particle size distribution within the abrasive grain, which varies depending on the desired properties and specific use of the abrasive grain. Typically, at least three (typically at least four, five, six, seven, eight, nine, ten, fifteen, twenty, thirty, or forty) of the largest abrasive particles in the abrasive grain of the present invention have substantially the same volume. In another aspect, at least three (typically at least four, five, six, seven, eight, nine, ten, fifteen, twenty, thirty, or forty) of the largest abrasive particles in the abrasive grain of the present invention may be greater than 20, 25, 30, 40, or even 50 micrometers in size. In another aspect, the plurality of abrasive particles may have at least a bi-modal distribution, and wherein the average particle size of a first distribution of the particles is at least 25 percent (more typically at least 100 percent, or even at least 200 percent) by volume larger than the average particle size of a second distribution of the particles.
In another exemplary embodiment, the present invention provides agglomerate abrasive grain comprising a plurality of sintered, crystalline abrasive particles bonded together via crystalline ceramic, metal oxide bonding material, wherein the agglomerate abrasive grain comprises, on a theoretical oxide basis, at least 85% by weight Al2O3, based on the total metal oxide content of the agglomerate abrasive grain; and wherein at least three of the largest abrasive particles are greater than 20 micrometers in size.
In addition to abrasive particle size and size distribution, the crystal size of the crystals within abrasive grain according to the present invention may vary as desired. Preferably, the abrasive particles of agglomerate abrasive grain according to the present invention are comprised of crystals (e.g., alpha alumina crystals) having an average crystal size less than 10 micrometers (preferably, less than 5 micrometers, more preferably, less than 1 micrometer).
In one exemplary embodiment, the present invention provides agglomerate abrasive grain comprising a plurality of sintered polycrystalline abrasive particles bonded together via crystalline ceramic, metal oxide bonding material, wherein the bonding material comprises, on a theoretical oxide basis, at least 50 percent by weight Al2O3, based on the total metal oxide content of the bonding material, wherein the crystalline abrasive particles are comprised of crystals having an average size less than 10 micrometers, and wherein at least three of the largest abrasive particles have substantially the same volume.
In another exemplary embodiment, the present invention provides agglomerate abrasive grain comprising a plurality of sintered, crystalline abrasive particles bonded together via crystalline ceramic, metal oxide bonding material, wherein the bonding material comprises, on a theoretical oxide basis, at least 50 percent by weight Al2O3, based on the total metal oxide content of the bonding material, wherein the crystalline abrasive particles are comprised of crystals having an average size less than 10 micrometers, and wherein at least three of the largest abrasive particles are greater than 20 micrometers in size.
The present invention also provides methods for making agglomerate abrasive grain. Embodiments of such methods includes those comprising contacting a plurality of particles (i.e., abrasive particles, precursor abrasive particles, or a combination thereof) with a precursor bonding material such that the particles agglomerate together (provides a precursor agglomerate abrasive grain)); and heating the agglomerated particles at at least one temperature for a time sufficient to convert the agglomerated particles into agglomerate abrasive grain according of the present invention. An example of suitable precursor abrasive particles for use in the methods of the present invention is boehmite-based particles. Exemplary precursor bonding materials include crystalline ceramic oxide precursor materials such as boehmite (e.g., boehmite sols, and optionally metal oxides (e.g., alumina) and/or precursors thereof (e.g., metal nitrates).
Further, for example, embodiments of agglomerate abrasive grain according to the present invention may be made by a method comprising:
contacting a plurality of at least one of abrasive particles or precursor abrasive particles with a precursor bonding material such that the particles agglomerate together; and
heating the agglomerated particles at at least one temperature for a time sufficient to convert the agglomerated particles into agglomerate abrasive grain comprising a plurality of abrasive particles bonded together with a sintered bonding material; wherein the sintered bonding material comprises, on a theoretical oxide basis, at least 50 percent by weight crystalline Al2O3, based on the total metal oxide content of the bonding material; and wherein the abrasive particles of the agglomerate abrasive grain have an average particle size of at least 5 micrometers.
Agglomerate abrasive grain of the present invention may also be made by a method comprising:
contacting a plurality of at least one of abrasive particles or precursor abrasive particles with a precursor bonding material such that the particles agglomerate together; and
heating the agglomerated particles at at least one temperature for a time sufficient to convert the agglomerated particles into agglomerate abrasive grain comprising a plurality of abrasive particles bonded together with a sintered bonding material; wherein the sintered bonding material comprises, on a theoretical oxide basis, at least 50 percent by weight crystalline Al2O3, based on the total metal oxide content of the bonding material; and wherein the heat-treated abrasive particles have a density of at least 85% of theoretical density, and the agglomerate abrasive grain has a porosity value of at least 10 percent.
Embodiments of agglomerate abrasive grain according to the present invention may be formed from abrasive particle, precursor abrasive particle, or combination thereof may be used in the methods of the present invention to form agglomerate abrasive grain. An exemplary method according to the present invention comprises:
contacting dried, boehmite-based precursor particles in the presence of liquid (e.g., water) such that a plurality of the precursor particles agglomerate together; and
heating the agglomerated particles at at least one temperature for a time sufficient to provide the agglomerate abrasive grain.
In some embodiments, it may be desirable to form an agglomerate abrasive grain, wherein the largest abrasive particles of the agglomerate abrasive grain have substantially the same volume. In these embodiments, the present invention provides a method for making agglomerate abrasive grain comprising a plurality of sintered, crystalline, alpha alumina-based abrasive particles bonded together via crystalline ceramic, metal oxide bonding material, wherein the bonding material comprises, on a theoretical oxide basis, at least 50 percent by weight Al2O3, based on the total metal oxide content of the bonding material, and wherein at least three of the largest abrasive particles have substantially the same volume, the method comprising:
contacting dried, boehmite-based precursor particles in the presence of liquid (e.g., water) such that a plurality of the precursor particles agglomerate together; and
heating the agglomerated particles at at least one temperature for a time sufficient to provide the agglomerate abrasive grain.
The present invention is directed to a method for making agglomerate abrasive grain comprising a plurality of sintered, crystalline, alpha alumina-based abrasive particles bonded together via crystalline ceramic, metal oxide bonding material, wherein the bonding material comprises, on a theoretical oxide basis, at least 50 percent by weight Al2O3, based on the total metal oxide content of the bonding material, and wherein at least three of the largest abrasive particles have substantially the same volume, the method comprising:
contacting dried, boehmite-based precursor particles in the presence of liquid (e.g., water) such that a plurality of the precursor particles agglomerate together;
drying the agglomerated precursor particles;
calcining the dried agglomerated precursor particles to provide porous agglomerated precursor particles;
impregnating the porous agglomerated precursor particles with a composition comprising liquid (e.g., water) and at least one of metal oxide or metal oxide precursor; and
heating the impregnated, agglomerated precursor particles at at least one temperature for a time sufficient to provide the agglomerate abrasive grain.
In some embodiments, it may be desirable to form an agglomerate abrasive grain, wherein the largest abrasive particles of the agglomerate abrasive grain are at least a given particle size. In these embodiments, the present invention provides a method for making agglomerate abrasive grain comprising a plurality of sintered, crystalline, alpha alumina-based abrasive particles bonded together via crystalline ceramic, metal oxide bonding material, wherein the bonding material comprises, on a theoretical oxide basis, at least 50 percent by weight Al2O3, based on the total metal oxide content of the bonding material, and wherein at least three of the largest abrasive particles are greater than 20 micrometers in size, the method comprising:
contacting dried, boehmite-based precursor particles in the presence of liquid (e.g., water) such that a plurality of the precursor particles agglomerate together; and
heating the agglomerated particles at at least one temperature for a time sufficient to provide the agglomerate abrasive grain.
The present invention also provides a method for making agglomerate abrasive grain comprising a plurality of sintered, crystalline, alpha alumina-based abrasive particles bonded together via crystalline ceramic, metal oxide bonding material, wherein the bonding material comprises, on a theoretical oxide basis, at least 50 percent by weight Al2O3, based on the total metal oxide content of the bonding material, and wherein at least three of the largest abrasive particles are greater than 20 micrometers in size, the method comprising:
contacting dried, boehmite-based precursor particles in the presence of liquid (e.g., water) such that a plurality of the precursor particles agglomerate together;
drying the agglomerated precursor particles;
calcining the dried agglomerated precursor particles to provide porous agglomerated precursor particles;
impregnating the porous agglomerated precursor particles with a composition comprising liquid (e.g., water) and at least one of metal oxide or metal oxide precursor; and
heating the impregnated, agglomerated precursor particles at at least one temperature for a time sufficient to provide the agglomerate abrasive grain.
In these embodiments, the present invention provides a method for making agglomerate abrasive grain comprising a plurality of sintered, crystalline, alpha alumina-based abrasive particles bonded together via crystalline ceramic, metal oxide bonding material, wherein the agglomerate abrasive grain comprises, on a theoretical oxide basis, at least 85% by weight alumina, based on the total metal oxide content of the agglomerate abrasive grain, and wherein at least three of the largest abrasive particles are greater than 20 micrometers in size, the method comprising:
contacting dried, boehmite-based precursor particles in the presence of liquid (e.g., water) such that a plurality of the precursor particles agglomerate together; and
heating the agglomerated particles at at least one temperature for a time sufficient to provide the agglomerate abrasive grain.
The present invention also provides a method for making agglomerate abrasive grain comprising a plurality of sintered, crystalline, alpha alumina-based abrasive particles bonded together via crystalline ceramic, metal oxide bonding material, wherein the agglomerate abrasive grain comprises, on a theoretical oxide basis, at least 85% by weight alumina, based on the total metal oxide content of the agglomerate abrasive grain, and wherein at least three of the largest abrasive particles are greater than 20 micrometers in size, the method comprising:
contacting dried, boehmite-based precursor particles in the presence of liquid (e.g., water) such that a plurality of the precursor particles agglomerate together;
drying the agglomerated precursor particles;
calcining the dried agglomerated precursor particles to provide porous agglomerated precursor particles;
impregnating the porous agglomerated precursor particles with a composition comprising liquid (e.g., water) and at least one of metal oxide or metal oxide precursor; and
heating the impregnated, agglomerated precursor particles at at least one temperature for a time sufficient to provide the agglomerate abrasive grain.
In yet other embodiments, it may be desirable to form agglomerate abrasive grain, wherein the agglomerate abrasive grain has a desired porosity value. In these embodiments, the present invention provides a method for making agglomerate abrasive grain comprising a plurality of sintered, crystalline, alpha alumina-based abrasive particles bonded together via crystalline ceramic, metal oxide bonding material, wherein the bonding material comprises, on a theoretical oxide basis, at least 50 percent by weight Al2O3, based on the total metal oxide content of the bonding material, and wherein the agglomerate abrasive grain has a porosity value in the range from 10 to 60 percent, the method comprising:
contacting dried, boehmite-based precursor particles in the presence of liquid (e.g., water) such that a plurality of the precursor particles agglomerate together; and
heating the agglomerated particles at at least one temperature for a time sufficient to provide the agglomerate abrasive grain.
The present invention also provides a method for making agglomerate abrasive grain comprising a plurality of sintered, crystalline, alpha alumina-based abrasive particles bonded together via crystalline ceramic, metal oxide bonding material, wherein the bonding material comprises, on a theoretical oxide basis, at least 50 percent by weight Al2O3, based on the total metal oxide content of the bonding material, and wherein the agglomerate abrasive grain has a porosity value in the range from 10 to 60 percent, the method comprising:
contacting dried, boehmite-based precursor particles in the presence of liquid (e.g., water) such that a plurality of the precursor particles agglomerate together; drying the agglomerated precursor particles;
calcining the dried agglomerated precursor particles to provide porous agglomerated precursor particles;
impregnating the porous agglomerated precursor particles with a composition comprising liquid (e.g., water) and at least one of metal oxide or metal oxide precursor; and
heating the impregnated, agglomerated precursor particles at at least one temperature for a time sufficient to provide the agglomerate abrasive grain.
Optionally, methods for making embodiments of agglomerate abrasive grain according to the present invention optionally include utilizing curable binder precursor material, ceramic binder precursor material in forming precursor agglomerate abrasive grain, and at least partially curing the ceramic binder precursor material when converting the precursor agglomerate abrasive grain into agglomerate abrasive grain according to the present invention.
The present invention further provides abrasive articles of manufacture. Agglomerate abrasive grain according to the present invention may be incorporated into various abrasive articles such as coated abrasives, bonded abrasives (including vitrified and resinoid grinding wheels), nonwoven abrasives, and abrasive brushes. The abrasive articles typically comprise agglomerate abrasive grain according to the present invention and binder.
Typically, agglomerate abrasive grain according to the present invention are sufficiently porous to advantageously allow binder to penetrate therein. This feature is particularly advantageous for coated and bonded abrasive articles. Further with regard to coated abrasives, preferred agglomerate abrasive grain according to the present invention can have a long life and relatively consistent cut rate. In another aspect, embodiments of agglomerate abrasive grain according to the present invention may be made having a desired level of porosity and/or bond strength between abrasive particles in order to provide preferential wearing of the agglomerate abrasive grain. Such preferential wearing of the agglomerate abrasive grain may be particularly desirable for bonded abrasive articles.
Alternatively, for example, agglomerate abrasive grain according to the present invention may be used as in loose form, including in abrasive slurries and as shot blast media.
The present invention also provides a method of abrading a surface, said method comprising:
contacting at least agglomerate abrasive grain according to the present invention, with a surface of a workpiece; and
moving at least of one the agglomerate abrasive grain or the surface relative to the other to abrade at least a portion of the surface with the agglomerate abrasive grain.
In this application:
xe2x80x9cCrystalline ceramic, metal oxide bonding materialxe2x80x9d refers to ceramic, metal oxide bonding material that is at least 60% by volume crystalline.
xe2x80x9cSubstantially the same volumexe2x80x9d means the volume of each relevant particle has a volume that is within fifty percent of the average volume of the relevant particles (i.e., if the three largest particles are to have substantially the same volume, each of the three largest particles have a volume that is within fifty percent of the average volume of the three largest particles);
xe2x80x9cAlpha alumina-based abrasive particle or bonding materialxe2x80x9d as used herein refers to an abrasive particle comprising, on a theoretical oxide basis, at least 50% by weight 10 Al2O3, wherein at least 40% by weight of the total amount of alumina is present as alpha alumina, based on the total metal oxide content of the particle or bonding material, respectively.
xe2x80x9cAbrasive particle precursorxe2x80x9d or xe2x80x9cunsintered abrasive particlexe2x80x9d refers to a dried dispersion (i.e., xe2x80x9cdried abrasive particle precursorxe2x80x9d) or a calcined dispersion (i.e., xe2x80x9ccalcined abrasive particle precursorxe2x80x9d), typically in the form of particles, that has a density of less than 80% (typically less than 60%) of theoretical, and is capable of being sintered or impregnated with an impregnation composition and then sintered to provide a sintered abrasive particle.
xe2x80x9cBoehmite-based precursor particlexe2x80x9d refers to a precursor abrasive particle comprising at least 50 by weight boehmite, based on the total solids content of the particle.
xe2x80x9cSinteringxe2x80x9d refers to a process of heating at a temperature below the melting temperature of the material being heated to provide densification and crystallite growth to provide a tough, hard, and chemically resistant ceramic material. Sintered abrasive particles are not made by a fusion process wherein heating is carried out at a temperature above the melting temperature of the material being heated.